1. Field of the Invention
The present invention relates to ground control and, more particularly, to a mathematical analysis and prediction of mine roof stability.
2. Description of the Prior Art
Identification of potential roof problems in coal mines has long been a complex issue due to the wide variety of mining and geological conditions. If a mine roof unexpectedly collapses, there could be a loss of life and an immediate halting of the mining. In particular, longwall mining techniques may be susceptible to cave-ins, especially at intersections between entries and crosscuts.
Mine roof falls may be related to many different factors, such as roof strata properties, sandstone channels, regional and localized horizontal stress, vertical stress and tectonic stress. In many instances, roof stability is a combination of these factors that cause roof problems.
Accordingly, a need remains for a method of predicting stable and unstable areas in a mine roof that takes into account the various factors that cause roof problems and that can be applied to various environments.
In accordance with the present invention, there is provided a method for determining the stability of a mine roof failure generally including the steps of identifying relevant factors that affect mine roof stability, quantifying and weighing each relevant factor, and calculating a roof instability rating (RIR) value based upon the quantified relevant factors. Primary and supplemental support systems may be determined based on calculated RIR values.
The step of calculating a mine roof instability rating based on weighted relevant influence factors is done by utilizing the mathematical equation RIR=xcexa3(Wi*FRi)/xcexa3Wi, where Wi are the numeric weight factors that individually correspond to a single one of the influence factors and FRi are the influence factors.
The influence factors are generally identified from geological formation and stresses, including sandstone rating factors, immediate roof rating factors, surface topographic factors, stress factors. Sandstone factors may include sandstone thickness, interval between sandstone and seam, existence of mica in sandstone. Immediate roof factors may include type, strength, and thickness of strata that comprise the immediate roof. Surface topographic factors may include stream valley, linear. Stress factors may include regional horizontal stress, localized horizontal stress, mining-induced horizontal stress, tectonic stress and vertical stress. The step of quantifying the influence factors may be accomplished through a step selected from the group including a finite element model, evaluating a core sample and evaluating a surface topography map. The step of weighting each influence factor may be accomplished by multiplying each influence factor by a numerical value that represents the impact of the respective influence factor in overall roof stability. The role of the respective influence factors in overall roof instability may be determined by a step selected from the group including observing mine roof conditions, evaluating actual mine roof failures, determine mine roof composition, and applying knowledge gained from other mine roof failures.